The advancement of electronic and communication technologies has supported a variety of services transceiving data between various devices and utilizing the transceived data. For example, the cloud computing service in which a user stores his or her personal information in a server and utilizes information of the server by using his or her terminal device has been actively used.
In such an environment, it is essential to use security technology to prevent data leakage. Accordingly, the server stores an encrypted data. In this case, it is necessary that encrypted data is decrypted every time the server searches data stored therein or performs a series of operations based on the data, and thus resources and time are wasted.
In addition, when a hacking of a third party is performed while the server performs decryption temporarily for computation, there is a problem that personal information can be easily leaked to the third party.
To resolve this problem, a homomorphic encryption method has been studied. According to a homomorphic encryption, even if a computation is performed in a ciphertext itself without decrypting encrypted information, it is possible to obtain the same result as a value obtained by performing computation of a plaintext and then encrypting the computed plaintext. Accordingly, various computations may be performed in a state that the ciphertext is not decrypted.
However, when an integer computation is performed according to a related-art homomorphic encryption method, there is a problem that the number of bits of the plaintext increases exponentially and the time required for the computation increases significantly.
Meanwhile, the related-art homomorphic encryption method has a drawback that an imaginary number part of a plaintext increases in a computation process. For example, since the related-art homomorphic encryption method performs homomorphic encryption of a message in a complex number space, an error is added to the imaginary number part even when a homomorphic encryption of a message of the real number space is performed. If a computation of a homomorphic encryption is repeated, an error of the imaginary number space gradually increases, and when an error of the imaginary number space is significantly increased, a message of a real number part corresponding to an actual message may be damaged in a homomorphic multiplication computation thereafter.
Accordingly, a method capable of improving a computation speed even in the state of a ciphertext and preventing the imaginary number part of the plaintext from being increased in the computation process is demanded.
The above information is presented as background information only to assist with an understanding of the disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the disclosure.